Patent GB-222204-A (GB)
Title: Improvements in party line telephones
IPC: H04Q5/00
Filed: 1923-06-26
Abstract: 222,204. Relay Automatic Telephone Co., Ltd., Bryant, G. H., Johnson, B. B., and Vanneck, R. G. June 26, 1923. Semi-automatic exchange systems.-In a system in which a number of two-wire subscriber's lines S<1>, S<3>, Fig. 1, are associated at a sub-exchange with a single common two-wire trunk J leading to a main manual exchange, Fig. 3, each line is provided with a connecting relay JNC for use both in incoming and outgoing calls, the circuits being such, however, that when one line has seized the trunk, every other line is prevented from gaining access to the busy trunk except when it is being called by the main-exchange operator. All sub-exchange connections are established by the operator by means of a temporarily-employed marking-selector, Fig. 5, of the well-known counting-relay type. As soon as the operator has plugged in, the release of the trunk is transferred to her control and the calling subscriber is asked to hang up but remains connected to the trunk. When the wanted line has been selected, both subscribers are rung and the calling subscriber waits until the cessation of ringing-current indicates that the called subscriber has replied. The system also provides means for interrupting a conversation in the event of a preferred call, and for dealing with faulty lines and apparatus, a distinctive signal being given to the calling subscriber and operator if a called line is faulty. Local call; seizure of trunk b calling subscriber; connection to operator. When subscriber S<1>, wishing to call subscriber S<3>, removes his receiver, his line relay completes circuit 3 for relays JNC, TCD in series. Relay A<1> energizes over the subscriber's loop and operates relay A1X, and relays TCD, A1X energize relay G which opens circuit 3 to prevent any other line from calling. Relay JNC locks up over circuit 8 in series with the cut-off relay CO which energizes relay F. Relav A1X connects battery at impedance coil B<2> to the upper trunk conductor and causes the lighting of the operator's lamp CL. The insertion of the answering plug in the jack A energizes relay B' which releases relay TCD and transfers the maintenance of a circuit for relay G to the control of the main-exchange. The operator, upon learning the wanted number, asks the subscriber to hang up when the release of relay A1X extinguishes lamp CL and energizes relay I which further maintains the energization of relay G. Selection of wanted line. The insertion of the dialling plug DP, Fig. 4, in the jack DJ connects relay I in series with the operator's dial over circuit 11, and completes circuit 12 for relay RP which locks up, energizes relay NUC and prepares the impulse responder, Fig. 5, at which relays B1.6 - - P5.0 energize in the usual manner. The transmission of three impulses, which are repeated by relay I, effects the operation of relay M3.8, and the subsequent release of relay DC1 completes marking-circuit 18 in which relay JNC3 energizes and connects the wanted subscriber S<3> to the trunk J. Relay SO energizes in the marking- circuit and operates relay SOX which releases relay NUC. The withdrawal of the dialling plug releases relay RP anl the impulse-responder. Ringing. Ringing-current from jack CJ is transmitted to the subscribers S<1>, S<3> over circuit 20. When the subscriber S<3> replies, relays A<1>, A1X energize to cut off the ringing current. Release. When both subscribers hang up, relays A<1>, A1X release, the cord-circuit supervisory lamp lights and the withdrawal of the plug releases relay G. Incoming call from main exchange. The insertion of dialling plug DP energizes relay I which operates relay G to mark the trunk J busy. The connection is established in the manner already described. Preferred call. If a conversation is in progress when the trunk J is required for a preferred call, the operator withdraws her plug from the jack A and inserts her dialling plug in jack DJ. The release of relay G unlocks the relays JNC which are at that time operated. The corresponding cut-off relays of the interrupted parties de-energize, and since their line relays are operated, their relays F remain locked up and hold open circuit 3 to prevent any interference from these parties. The party wanted for the preferred call is selected in the manner already described. Called line faulty. If relay F is operated due to a line being faulty, no marking circuit is completed, relay SOX is not energized, and upon the release of relay RP relay NUC connects a differentially-wound buzzer NU to the trunk J. Faulty sub-exchange apparatus. The battery connections marked by an asterisk are supplied through a relay FA which is short-circuited by relay G when the trunk is in use. If therefore any current is passing when the trunk is not in use, relay FA connects battery to the upper trunk conductor to light the operator's lamp CL. In a similar manner the blowing of a fuse Z lights the lamp CL.